Use of handset microphone to enhance speakerphone loudspeaker performance

ABSTRACT

A speakerphone incorporates a portion defining a loudspeaker cavity, the cavity containing a loudspeaker. The speakerphone also includes a handset with an internal microphone in the handset. The speakerphone has a housing adapted to receive the handset, and when it is thus received, the handset microphone is acoustically coupled to the loudspeaker cavity, allowing the handset microphone signal to be used to control feed-back or feed-forward algorithms that enhance the performance of the speakerphone.

[0001] This invention relates generally to an improvement for enhancingthe acoustical performance of the speakerphone in sets, and takesadvantage of the fact that the handset microphone is normally availableand unused when the speakerphone loudspeaker is utilized.

BACKGROUND OF THIS INVENTION

[0002] To control loudspeaker variability, some manufacturers test everyloudspeaker in their production. This test ensures a nominal speaker andenclosure variability. A reasonably large tolerance window or high costloud speaker is required to obtain a reasonable pass rate.

[0003] To boost speaker performance, electrical equalisation is oftenapplied. However, this can only be an average curve since individualadjustment would be prohibitively expensive.

[0004] At high power levels or any other times where a speaker mayexhibit non-linearities, few if any inexpensive solutions exist. Onesolution in high power, high performance systems is to mount anaccelerometer on the speaker driver, and use a feedback system tolinearise the driver. Myers discloses such a system in U.S. Pat. No.3,798,374, issued on Mar. 19, 1974.

[0005] In attempting to avoid such costs, other convoluted circuitry hasbeen used to monitor the drive signal of the loudspeaker. This addedcircuitry adds to the expense and a great deal must be known about thedriver before it can yield any useful information. Bai and Wu describesuch a circuit in “Robust Control of a Sensorless Bass-EnhancedMoving-Coil Loudspeaker System”, J. Acoust. Soc. Am. 105(6) pp.3283-3289.

[0006] It is evident that, if one wants to avoid non-linearities(adaptive acoustic echo cancellers do not tolerate them), a cost penaltyis imposed. This cost penalty comes about either as increased componentcost, increased test time, reduced production yield, extra transducers,or extra circuitry. Even with these extra costs, non-linearities areunavoidable since clipping, buzzes and rattles are still possible.

GENERAL DESCRIPTION OF THIS INVENTION

[0007] An aspect of the present invention is the ability to compensatefor loudspeaker variability, enclosure variability, and non-linearitiesin the circuitry and the loudspeaker. A further aspect is the ability toenhance the loudspeaker performance at low frequencies and high power.Still further, the invention can enhance the performance of acousticecho cancellers used in full-duplex speakerphones. These aims areattained by using existing telephone hardware with the addition of anacoustical waveguide (acoustic coupling) which is expected to be a veryinexpensive part.

[0008] The unique aspect of this invention is its use of existingtransducers and circuitry to provide feed-back or feed-forward controlof one or more circuit or hardware characteristics. The latter couldinclude a loudspeaker itself, the acoustic echo canceller, a voicerecognition system (if present) and any other hands-free telephonyoperation that could be improved by the use of such a signal.

[0009] The handset is rarely in use while the loudspeaker is emittingsound. If the loudspeaker cavity is coupled to the handset microphone,it becomes possible to use the signal created at the microphone tocontrol various feed-back or feed-forward algorithms that enhance theperformance of the speakerphone. The handset typically has its ownCODEC, so that the only part that is not already implemented on mosttelephones is an acoustic coupler between the handset microphone and theloudspeaker cavity. The provision of such acoustic coupler is simple andcheap.

[0010] One of the side benefits to be gained from this improvementinvolves designing the waveguide so as to provide an elastomeric sealagainst the handset. By doing so it is possible to minimize thelikelihood of the handset rattling when the loud speaker is inoperation.

[0011] More particularly, this invention provides, in a speakerphonehaving a portion defining a loudspeaker cavity containing a loudspeaker,the speakerphone including a handset having an internal microphone, saidportion of the speakerphone defining means for receiving the handset,the improvement comprising acoustically coupling the handset microphoneto said loudspeaker cavity, so that the resulting handset microphonesignal can be used to control feed-back or feed-forward algorithms thatenhance the performance of the speakerphone.

[0012] Furthermore, this invention provides, in a speakerphone having aportion defining a loudspeaker cavity containing a loudspeaker, thespeakerphone including a handset with a handset cavity enclosing aninternal microphone, said portion of the speakerphone defining registrymeans for receiving the handset, the improvement comprising couplingmeans for acoustically coupling the handset microphone to saidloudspeaker cavity whenever the handset is received by said registrymeans, so that the handset microphone signal can be used to controlfeed-back or feed-forward algorithms that enhance the performance of thespeakerphone.

[0013] Still further, this invention provides a speakerphone comprising

[0014] a portion defining a loudspeaker cavity,

[0015] a loudspeaker within said cavity,

[0016] a handset,

[0017] an internal microphone in the handset,

[0018] means on said portion of the speakerphone for receiving thehandset, and coupling means for acoustically coupling the handsetmicrophone to said loudspeaker cavity, so that the handset microphonesignal can be used to control feed-back or feed-forward algorithms thatenhance the performance of the speakerphone.

[0019] Again, this invention provides, for a speakerphone having aportion defining a loudspeaker cavity containing a loudspeaker, thespeakerphone including a handset having an internal microphone, saidportion of the speakerphone defining receiving means for receiving thehandset, a method of exerting control over at least one aspect of thecircuitry of the speakerphone, comprising acoustically coupling thehandset microphone to said loudspeaker cavity whenever the handset isreceived by the receiving means, and using the resultant microphonesignal to accomplish such control.

[0020] Yet further, this invention provides, for use with a speakerphonehaving a portion defining a loudspeaker cavity containing a loudspeaker,the speakerphone including a handset with a handset cavity enclosing aninternal microphone, said portion of the speakerphone defining receivingmeans for receiving the handset:

[0021] a method of controlling at least one aspect of the speakerphonecircuitry, comprising acoustically coupling the handset microphone tosaid loudspeaker cavity whenever the handset is received by thereceiving means, and using the resultant microphone signal to controlfeed-back or feed-forward algorithms that enhance the performance of thespeakerphone.

GENERAL DESCRIPTION OF THE DRAWINGS

[0022] One embodiment of this invention is illustrated in theaccompanying drawings, in which like numerals denote like partsthroughout the several views, and in which:

[0023]FIG. 1 is a block diagram for a typical telephone;

[0024]FIG. 2 is a simplified sectional view through a handset and aloudspeaker cavity, showing the location of the essential components;

[0025]FIG. 3 is a simplified block diagram of a typical speakerphoneset; and

[0026]FIG. 4 is a modified block diagram illustrating the use of thehandset signal as the control signal for an acoustic echo canceller.

DETAILED DESCRIPTION OF THE DRAWINGS

[0027] Attention is first directed to FIG. 1, showing a block diagram ofa typical telephone. For illustration purposes, many blocks are shown.In an actual implementation, however, they could comprise either aplurality of devices or a device which incorporates a plurality ofblocks. Similarly, the busses 36, 37, 38, 39, 40 may either all beseparate busses, or be combined together as the designer sees fit.

[0028] For purposes of the present disclosure, the line 20 and itsinterface 32 can either be analogue PSTN, digital TDM, wireless,switched packet (e.g. VoIP, ATM) or any other voice carrier lineinterface.

[0029] Typically, the controller 33 directs either or both voicechannels to the line interface 32 via the audio bus 36 to and from theappropriate transducers and processing. The DSP 34 typically providesvolume control, speakerphone functionality, tone generation, and othernecessary functionality for the operation of the telephone.

[0030] In FIG. 2, functional blocks are illustrated to help understandthe operation of the invention. In this figure, the handset 1 has amicrophone 4 which is acoustically coupled through an acousticallydesigned waveguide 15 to the cavity 16 in the speaker set 10 where theloud speaker 11 is housed. The resulting signal generated by themicrophone is amplified by the handset microphone preamplifier 5, passesto its CODEC 30 and is sent to the DSP 34 via the audio bus 36. Asstated above, the acoustical waveguide 15 is the only component notalready found in current telephones. This waveguide, in its simplestform, would be a soft elastomeric grommet dressing a hole 17 that linesup with the handset microphone port 18.

[0031] Within the DSP function 34, appropriate algorithms areimplemented that compensate for the actual loud speaker 11 performancewithin the set 10. These algorithms typically modify the receive signalfrom the line 20 before they are sent out to the speaker CODEC 31.

[0032] The following are possible algorithms that could utilize thistype of signal to advantage:

[0033] 1. Loudspeaker Linearisation

[0034] In this implementation, the microphone signal is used to correctthe loudspeaker's frequency response and possible non-linearities. Onehas to determine, a priori, the transfer function between the desiredacoustic signal (usually at 0.5 m in the position described in ITUP.340) and the sound pressure in the loudspeaker cavity. This transferfunction is further coloured by the frequency response of the handsetmicrophone 4 and the acoustic waveguide 15. By applying the inverse ofthis transfer function to the microphone signal, one can then use thissignal as a feed-back signal to control an adaptive filter which willcompensate for any deviations. This will compensate for loudspeakervariations, and for loudspeaker and circuitry non-linearities, and couldenhance the performance of the loudspeaker (e.g. bass boost). Making theenclosure less critical may reduce the cost of the enclosure.

[0035] 2. Acoustic Echo Canceller Control Signal

[0036] In a conventional full-duplex speakerphone, the loudspeaker andits driver are assumed to have perfectly linear characteristics. In thedesign of the set, much attention is paid to ensure that this assumptionis in fact reasonably correct. Within the algorithm the signal islimited so as to be well below any circuitry non-linearity (e.g. belowclipping), thus reducing the dynamic range or pre-distortion of thesignal (illustrated in FIG. 3).

[0037] Using the actual end receive signal would solve these problems.In this implementation, if we use the handset microphone signal andcorrect it as described above, we will have a very close approximationto the real signal (see FIG. 4). One now has a control signal that islinearly related to the real receive signal and to the receive signalthat the hands-free microphone sees. (The echo canceller is trying toestimate the room impulse response based on the receive signal. In orderto do this reasonably successfully, perfect linearity must be assumed.)If significant set non-linearities occur, such as buzzing or rattling,the handset microphone will also pick this up and they will notdestabilise the echo canceller.

[0038] 3. Microphone to Speaker Separation Enhancement

[0039] In Canadian Patent Application No. 2,229,424, a secondarymicrophone was placed in the cavity of the telephone set. The signalfrom this microphone was used to increase the separation between theloudspeaker signal and the hands-free microphone. The major drawbackswere cost and the fact that this solution was approximate (varied fromset to set). By the use of the handset microphone coupled to the speakercavity as described above, it is now possible to implement this ideawith greater success. Specifically, the analogue circuit described inthe disclosure of Robert McLeod can be utilized. However, the use ofdigital adaptive filters provides better performance without any extraparts costs.

[0040] 4. Double Talk Detection Enhancement

[0041] A more efficient double talk detector is made possible by thisdevelopment. In single talk receive, the signal between the handsetmicrophone and the hands-free microphone will be perfectly correlatedexcept for the room ambient noise. In single talk transmit, they willalso be highly correlated as the handset microphone can still (to asignificantly lesser extent) capture the ambient acoustical noise.However, in double-talk, the correlation will significantly degrade asthe receive signal will dominate the handset microphone signal and thetalker in the room should significantly affect the hands-free microphonesignal. Accurate estimation of the double talk condition is critical toa stable acoustic echo canceller.

OTHER VARIATIONS

[0042] In an analogue set, the signals could be processed using analoguecircuitry. This would likely prove to be less cost effective, but iswell within the intent of the present developments.

[0043] As well, it is expected that the use of this device would improveimplementation of an ultrasonic hook switch, as set forth in Mitel U.K.patent application filed Sep. 7, 2000.

[0044] Algorithms used in the performance enhancements described abovecan be enabled when the hookswitch detection signal 41 (FIG. 1) indictates to the software running in controller 33 that the handset is inits cradle. This is important to note because the user of the handsetcould press a speakerphone button on the keyboard 13, while holding thehandset. The software implements the enhancing algorithms only when thehandset has been returned to its cradle (as indicated by the hookswitchsignal 41). This ensures stable algorithm handling within the DSP 34.

[0045] While one embodiment of the present invention has beenillustrated in the accompanying drawings and described herein above, itwill be evident to those skilled in the art that changes andmodifications may be made therein without departing from the essence ofthe present invention, as set forth in the appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. In a speakerphone havinga portion defining a loudspeaker cavity containing a loudspeaker, thespeakerphone including a handset having an internal microphone, saidportion of the speakerphone defining means for receiving the handset,the improvement comprising acoustically coupling the handset microphoneto said loudspeaker cavity, so that the resulting handset microphonesignal can be used to control feed-back or feed-forward algorithms thatenhance the performance of the speakerphone.
 2. In a speakerphone havinga portion defining a loudspeaker cavity containing a loudspeaker, thespeakerphone including a handset with a handset cavity enclosing aninternal microphone, said portion of the speakerphone defining registrymeans for receiving the handset, the improvement comprising couplingmeans for acoustically coupling the handset microphone to saidloudspeaker cavity whenever the handset is received by said registrymeans, so that the handset microphone signal can be used to controlfeed-back or feed-forward algorithms that enhance the performance of thespeakerphone.
 3. The improvement claimed in claim 2, in which saidloudspeaker cavity is defined at least in part by a wall, and in whichsaid coupling means comprises an opening through said wall which isaligned with said internal microphone when the handset is received bysaid registry means.
 4. The improvement claimed in claim 3, in which thecoupling means further comprises an elastomeric grommet dressing thehole, the grommet extending sufficiently far from the wall to contactthe handset when the latter is received by said registry means, thusdampening handset movement and minimizing the risk that use of theloudspeaker will cause the handset to rattle.
 5. A speakerphonecomprising a portion defining a loudspeaker cavity, a loudspeaker withinsaid cavity, a handset, an internal microphone in the handset, means onsaid portion of the speakerphone for receiving the handset, and couplingmeans for acoustically coupling the handset microphone to saidloudspeaker cavity, so that the handset microphone signal can be used tocontrol feed-back or feed-forward algorithms that enhance theperformance of the speakerphone.
 6. The speakerphone claimed in claim 5,in which the handset defines a handset cavity containing said handsetmicrophone.
 7. The improvement claimed in claim 5, in which saidloudspeaker cavity is defined at least in part by a wall, and in whichsaid coupling means comprises an opening through said wall which isaligned with said internal microphone when the handset is received bysaid registry means.
 8. The improvement claimed in claim 7, in which thecoupling means further comprises an elastomeric grommet dressing thehole, the grommet extending sufficiently far from the wall to contactthe handset when the latter is received by said registry means, thusdampening handset movement and minimizing the risk that use of theloudspeaker will cause the handset to rattle.
 9. For a speakerphonehaving a portion defining a loudspeaker cavity containing a loudspeaker,the speakerphone including a handset having an internal microphone, saidportion of the speakerphone defining receiving means for receiving thehandset, a method of exerting control over at least one aspect of thecircuitry of the speakerphone, comprising acoustically coupling thehandset microphone to said loudspeaker cavity whenever the handset isreceived by the receiving means, and using the resultant microphonesignal to accomplish such control.
 10. For use with a speakerphonehaving a portion defining a loudspeaker cavity containing a loudspeaker,the speakerphone including a handset with a handset cavity enclosing aninternal microphone, said portion of the speakerphone defining receivingmeans for receiving the handset: a method of controlling at least oneaspect of the speakerphone circuitry, comprising acoustically couplingthe handset microphone to said loudspeaker cavity whenever the handsetis received by the receiving means, and using the resultant microphonesignal to control feed-back or feed-forward algorithms that enhance theperformance of the speakerphone.
 11. The improvement claimed in claim 9,in which said loudspeaker cavity is defined at least in part by a wall,and in which said coupling means comprises an opening through said wallwhich is aligned with said internal microphone when the handset isreceived by said receiving means.
 12. The improvement claimed in claim11, in which the coupling means further comprises an elastomeric grommetdressing the hole, the grommet extending sufficiently far from the wallto contact the handset when the latter is received by said receivingmeans, thus dampening handset movement and minimizing the risk that useof the loudspeaker will cause the handset to rattle.